The invention relates to a plastics package of the type stated in the introductory portion of claim 1, wherein a snap engagement is provided during the application of a lid to a container. Such a package is known e.g. from U.S. Pat. No. 5,143,219.
There is a need for providing a low-cost package that is suitable for the transport of e.g. inflammable liquids. In particular, there is a need for such a package as can meet the strict demands made by the UN with respect to density, both at an internal positive pressure of 1 bar liquid pressure and 0.4 bar gas pressure as well as after a drop test where the lid of the package is affected by a concentrated external impact. Even though for years numerous attempts have been made at providing such packages of plastics (see e.g. U.S. Pat. No. 5,163,576), so far it has nevertheless been necessary to resort to metallic packages in practice to ensure reliable properties. It has thus been observed that the radial expansion of the known plastics containers combined with the tendency of the plastics layer to bulge upwards during relatively low internal pressures has given rise to release of the snap engagement, so that the mentioned UN specifications cannot be met.
The invention has made it possible to provide a low-cost package which can be made of a plastics material in a simple manner, and which meets the mentioned specifications.
This is achieved as stated in claim 1, wherein, during the establishment of a snap engagement between the lid and the container of the package, first a compression and then a partial relief of a sealing member embedded between the lid and the container are provided. This greatly obviates the situation that an internal pressure in the container and an external impact can cause the snap engagement to be released. When preferably the lid and the container are formed with inclined cooperating engagement faces, a particularly simple structure is achieved.
As stated in claim 5, the sealing member is preferably arranged in the lid, whereby damage to the sealing member during the application of the lid to the container is avoided to the greatest extent possible.
When the package is formed so as to provide a ring-shaped space, as stated in claim 6, a particularly effective sealing of the package is achieved.
The invention moreover relates to a lid for a container for providing a package of the type stated initially. The invention also relates to an expedient mould for the manufacture of the lid.